What Is the Difference Between Sidewalk Chalk & Chalkboard Chalk?

Sidewalk chalk is made from the mineral gypsum. (Image: sidewalk chalk image by Jeffrey Sinnock from Fotolia.com)

Sidewalk chalk is used outdoors and washes away with water. Chalkboard chalk is used in instructional settings and removed with a special eraser. There are a few key differences between sidewalk chalk and chalkboard chalk, despite their similar ingredient.

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History

Sidewalk chalk and chalkboard chalk were once made of calcium carbonate. Calcium carbonate is a type of soft limestone that forms underwater. Sidewalk chalk and chalkboard chalk are now made from the mineral calcium sulfate, or gypsum, explains the Earth Science Picture of the Day website.

Differences

Chalkboard chalk is approximately .35 of an inch in diameter and 3.15 inches long. Sidewalk chalk, on the other hand, is typically larger in length, thicker and comes in an array of colors.

The American National Standards Institute determines chalk size for use in the classroom. (Image: Multicolored chalks image by Sergey Kolesnikov from Fotolia.com)

Function

Sidewalk chalk and chalkboard chalk have different functions. Sidewalk chalk is chiefly used in artistic applications with asphalt and cement being the canvas of choice. Chalkboard chalk is primarily found on chalkboards to convey text.

Most people are familiar with chalkboard chalk from their school days. (Image: chalk board image by Brett Bouwer from Fotolia.com)